August 26, 2026
This week’s photo is courtesy of WellJet HPC- Camarillo, CA, USA
Safety Focus
Part 3 of 4: Silica and Respirable Dust: Control It
Now it is time to focus on how to protect your lungs.
Silica dust is not always obvious. A little visible dust may mean your controls need attention, and the fine dust that does the damage can be hard to see. The goal is simple: keep dust out of the air before it reaches anyone’s breathing zone.
OSHA gives construction contractors two ways to handle silica. The easiest place to start is Table 1. It covers common dust-producing tasks and tells you what controls, work practices, and respiratory protection are required. If your task is listed and you fully follow the controls shown, you do not have to conduct separate exposure monitoring for that task.
If the task is not on Table 1, or if you cannot fully follow the listed controls, you move to the alternative method. That means assessing the exposure and using workable controls to get it as low as possible. OSHA’s limit, called the PEL, is 50 micrograms of respirable silica per cubic meter of air, averaged across an 8-hour shift.
In the field, controlling the dust usually starts with water or dust collection. Wet methods put water where the dust is made, helping keep it down on saws, drills, and grinders. Dust collection uses a shroud or hood and a vacuum or collector to pull dust away from the worker. For some Table 1 tasks, the dust collector must have a filter that is at least 99 percent efficient and a filter-cleaning mechanism. Keep the hoses clear, check connections, and follow the dust-control equipment manufacturer’s instructions.
Housekeeping is part of the control plan. Do not dry sweep or dry brush silica dust if a wet method, HEPA-filtered vacuum, or another dust-minimizing method will work. Avoid blowing dust off clothes, tools, or work areas with compressed air unless the dust is being captured by effective ventilation or another cleaning method is not feasible.
Two numbers are worth remembering. The PEL is 50 micrograms per cubic meter over an 8-hour shift. The action level is 25 micrograms per cubic meter over the same period. Under the alternative method, the action level is the point where an employer may need to assess exposure. Medical surveillance has a different trigger: it must be offered to employees who are required to wear a respirator under the silica standard for 30 or more days in a year.
Respirators matter, but they are not the first move. Use the water, dust collection, work practices, and controls the task calls for. Then use respiratory protection when Table 1 requires it or when controls alone cannot keep exposure below the PEL.
Before starting a silica-producing task, check Table 1, check the equipment, and make sure the crew knows the plan. That is how you keep dust from becoming the part of the job that follows someone home.
KEY TAKEAWAYS
• Start with the dust control listed for the task. Water and dust collection come before relying on a respirator.
• If the task is on OSHA Table 1 and you fully follow its requirements, separate exposure monitoring is generally not required.
• The PEL is 50 micrograms per cubic meter. The action level is 25. Both are based on an 8-hour shift.
• Do not dry sweep or blow silica dust around when a wet method, HEPA vacuum, or effective dust capture can do the job.
• Check the tool, hose, water supply, vacuum, and control plan before the work starts.
Sources:
Knowledge Share
Part 3 of 4: Aquifer Hydraulics and Math: Apply It
Yesterday, we talked about hydraulic conductivity, or K. Think of K as a way to describe how easily water moves through the formation.
One quick way to get a starting number is with a sieve test. Take a sand sample, run it through a set of sieves, and look at the grain-size curve. The number often used is called D10. In plain language, it is the grain size where 10 percent of the sample is finer.
For clean sand, the Hazen equation can turn that D10 number into a rough K estimate:
K = C × D10²
You do not need to do the math in the field to understand the takeaway: coarser, cleaner sand usually lets water move more easily than finer sand with silt or clay mixed in.
For example, a clean sand with a D10 of 0.2 mm can work out to roughly 35 meters per day, or about 115 feet per day, using one common version of the equation. That is a useful first look at what the formation might do. It is not a yield guarantee.
There is a catch. Hazen works best on clean sand that is fairly uniform. It is not a good fit for clayey material, silty sand, mixed gravel, or formations that change a lot from one depth to the next. And that is common drilling reality. A good-looking sand sample from one interval does not prove the whole screen zone will perform the same way.
That is why field testing matters.
A slug test is a quick way to see how water level recovers in a well after a known change. It gives a local read on the formation around that screened interval. A pumping test goes further. It shows how the aquifer responds while the well is being worked and can reveal whether the formation will support the expected rate over time.
The practical rule is simple: use sieve data to help understand the formation and guide early decisions. But if the number will drive screen size, filter-pack selection, or a promised production rate, back it up with field data.
The formation does not care what the sieve curve says. It will tell you what it can produce when you test it.
KEY TAKEAWAYS
• A sieve test gives a quick first estimate of how easily water may move through clean sand.
• Coarser, cleaner sand usually moves water more easily than fine sand, silt, or clay.
• Hazen is an analysis tool, not a yield guarantee.
• Slug tests check a small area around the screen. Pumping tests show how the aquifer responds under load.
• Before a K value drives screen selection, filter-pack design, or a yield estimates, confirm it with field testing.
Sources:
• U.S. Geological Survey: Ground-Water Flow Directions and Estimation of Aquifer Hydraulic Properties
Recommended Print References:
• Handbook of Ground Water Development- Roscoe Moss Company
• Groundwater & Wells, Third Edition- Edited by Robert J. Sterrett, Johnson Screens
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